18.4-38 vs 20.8 34 December 16, 2010 02:35PM
have a jd syncro need to go from 7th to 8th to compete with quads & tourqes in 3000rpm to get threw holes from 4x4s ahaed of our class is it best to go with 18.4 38 on 20in or 20.8 34 on 20-22 in rim to get speed i have enough in 7th with 18.4 38s but 8th is a big jump i know about the 71/2 gear but would like to find easer way thanks.
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Re: 18.4-38 vs 20.8 34 December 16, 2010 03:35PM
The 20.8 34's are a little bit shorter,probably 2 maybe 3 inches.Probably won't gear you down as much as you need,but it would help.
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Re: 18.4-38 vs 20.8 34 December 16, 2010 10:34PM
18.4-34 to 18.4-38 should be about 3 3/4" difference. Depending on tread wear, 20.8-34 and 18.4-38 there is very little difference, I believe 1" or less.
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Re: 18.4-38 vs 20.8 34 December 17, 2010 12:17AM
I have set of 20.8-34's and they are higher the 18.34-38's that I am currently running. If you are going to run 8th you're going to need some real HP. Have you ever tried 8th with your current setup?
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Re: 18.4-38 vs 20.8 34 December 17, 2010 08:22AM
i can run 8th in 9000 and 9500 fine but most of my hooks are 12000 & 14000 with tractor at 11,500 in 7th plenty of power just afraid 8th will be to big of a jump would it be a good ideal to try running tractor at 9500 lbs in 8th for 12000 lbs class thanks
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Re: 18.4-38 vs 20.8 34 December 17, 2010 11:17AM
I've tried that (20.8 x 34s, 20 inch rims) with a 619 deere, and should have stayed with my original "concrete" hard 20.8 cooper's that came on the tractor. Could handle 7th gear at any wt I tried, didn't have the fuel/air mods to pull 8th at 11000. Another option could be bolting on a set of scraper planetaries---moving seventh gear up to near a true 7.75 gear, 3 or so mph slower than 8th. Down side to that change, 8th gear gets VERY FAST, up about 30%, as discussed on this site in recent weeks.
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Re: 18.4-38 vs 20.8 34 December 17, 2010 11:37AM
just re-read original post---if greenman is running a sb deere, changing to a 7 1/2 might be the cheapest option, but their are many sbjd cases out there with three speed units that are close ratio units near 8th gear, that could meet his needs long term---if his budget and long term pulling plans point to that end. Anything causing you to lose "footprint", with the power you already have, would not be beneficial.
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Re: 18.4-38 vs 20.8 34 December 17, 2010 01:25AM
20.8X34 HAS A ROLLING DIAMETER OF 203 " 18.4X38 HAS 206" AXLE HEIGHT 20.8X34 IS 31.1" 18.4X38 IS 30.9" IT WOUILD BE A WASTE OF TIME AND MONEY THERES HARDLY ANY DIFFERENCE IN THE TO TIRES
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Re: 18.4-38 vs 20.8 34 December 17, 2010 02:00PM
How much differance in size is a 20.8 38 vs. an 18.4 42
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Re: 18.4-38 vs 20.8 34 December 17, 2010 03:24PM
A 20.8X38 HAS THESE FACTS 32.4 AXLE HEIGHT 212 " ROLLING CIRCUM. AND 380 SQ IN ON THE GROUND 18.4X42 HAS 33.3 AXLE HEIGHT 217 ROLLING CIRCUM. AND 345 SQ IN ON THE GROUND
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Re: 18.4-38 vs 20.8 34 December 18, 2010 04:03AM
don't weight up all the way and run 8th gear. your speed and momentum will carry you farther than going slower weighted down.
I've ran this way and for more than a year weighing more than 3500 less than max weight. you also can keep your tractor balanced better because your not always switching classes. just my 2 cents good luck
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Re: 18.4-38 vs 20.8 34 December 18, 2010 08:11AM
ever try 20.8-38 and just stay in 7th
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